Your average kid knows that if a skink lizard looses a tail it will eventually grow another one. Moreover, it is well understood among children and grown-ups who make a habit of studying such things that many lower animals are capable of regenerating quite complex structures, including whole limbs and organs following injury. For example, fish are able to grow back a heart after a significant part of the old heart of the fish had been sliced away (Poss et al., 2002). This is an astounding result when one reflects on how essential the heart is to the minute-to-minute survival of most animals.
However, regeneration of tissue, limbs and organs following injury in people is not as straightforward as it is in fish. While human tissues damaged by mechanical wounding, disease processes and other causes are capable of healing, complex tissue structure and function is rarely, if ever wholly restored. Instead, recovery of nearly all tissues from injury in humans and other higher vertebrates is dominated by the formation of scar tissue. The most familiar example of this is the discolored and fibrotic scars that linger following the healing of a skin cut or graze. Less well appreciated is that formation of glial scar tissue following injury to the brain or spinal chord is one of the main obstacles to restoration of neural function following damage to the central nervous system (Silver and Miller J H, 2004). There is currently no means of treating or preventing such scarring and promoting the regeneration of complex tissue structure and function following injury.